1. Field of the Invention
The invention relates to a method and a device for magnetron sputtering. These technologies are used for depositing functional and finishing layers. Magnetron sputtering technologies are already used on a large scale in industrial production, e.g., for coating architectural glass.
2. Discussion of Background Information
Coating processes in which the coating is composed of several chemical elements, e.g., titanium dioxide, are of particular technical importance. With coating processes of this type, the metallic component is often provided by sputtering a metallic target. The other layer component is introduced into the process chamber in a gaseous form. High coating rates and optimal layer quality can only be achieved with these reactive coating processes when the process is operated in the area of unstable operating points (i.e., in the transition mode). This transition mode is characterized in that the reactive gas feed is large enough to provide a sufficient amount of reactive gas for the layer deposit while at the same time being so low that a contamination of the sputter target with reactive gas is avoided. Particularly with these unstable operating points, constant quality and reproducibility of the coating require the magnetron sputtering system to be operated with the aid of complex control loops.
According to the prior art, magnetron sputtering sources can be influenced through the electric power fed or the reactive gas flow. The necessary control signal can be obtained by measuring different parameters. Thus, for example, it is proposed in EP 1 232 293 B1 to use the harmonic content of the electric parameters of the discharge as a control variable.
Additionally, it is known from EP 0 795 623 A1 to determine the partial pressure of reactive gases with suitable probes. Thus, for example, the oxygen partial pressure measured with a lambda probe can be used as a control variable. Also, it is known from J. Affinito et al., J. Vac. Sci. Technol. A 2 (1984), p. 1275-1284, to control a magnetron sputtering source by measuring the plasma impedance. As a further possibility, the dissertation by J. Strümpfel, Prozessstabilisierung beim reaktiven Hochratenzerstäuben mittels optischer Emissionsspektroskopie zur industriellen Herstellung von Indium-Zinn-Oxidschichten und Titandioxidschichten, Chemnitz 1991, describes the measurement of the intensity of selected spectral lines of the plasma of the magnetron sputtering sources.
Furthermore, the deposition rate of a magnetron sputtering source that is operated in the unstable transition range is not absolutely known. As such, the layer thicknesses of the layers produced on the substrate have to be determined after deposition. Optical measurements such as photometry or ellipsometry are primarily used to this end.
The described expenditure in terms of equipment for each individual sputtering source of a coating system is necessary in order to ensure a constant layer quality, a constant layer structure and a constant layer thickness. This results in high costs in acquiring and operating the coating system, as well as in a high susceptibility to damage, particularly in large in-line systems.
The coating of steel band substrates or architectural glass is carried out in continuous process on an industrial scale with in-line systems of this type. Such coating systems have a large number of magnetron sputtering sources. Twenty to approximately thirty sources are typical; however, systems with up to sixty magnetron sputtering sources are also in use. Accordingly, what is critical for industrial production is the interaction of all of these individual sputtering sources, whereby several sources often deposit one and the same material. Only through very great expenditure is it possible for all the sources to supply identical results with respect to layer properties, coating rate and homogeneity.
An optical measurement of the layer properties after each sputtering source has proven to be extraordinarily difficult. Such methods are inapplicable in practice with overall systems having a plurality of optical measuring systems due to high costs and high susceptibility to damage.